1. Field of the Invention blind fastener that can be readily adapted to interconnect a wide variety of objects and structural elements.
2. Description of the Background Art
Over the years, a vast array of fasteners have been proposed, with each being cited as having one or more advantages that make it suitable for a given application or installation. In situations where the user lacks convenient access to one side of the structural components to be joined, however, the options are somewhat limited. Fasteners installed in structural members such as hollow walls, for example, typically comprise a threaded member, such as a bolt or screw, and an anchoring mechanism. Rotation of the threaded member causes the anchoring mechanism to expand and contact the inside of the wall to anchor the fastener in place. Common examples of such fasteners are the so-called "toggle" bolts and "moly" bolts.
One problem associated with blind fasteners of the aforementioned type is that a portion of the anchoring mechanism is usually received within the hole in the wall through which the fastener is inserted. Therefore, stress exerted by heavy objects attached to the fastener on the outside of the wall may cause the fastener to pull outwardly through the opening. Another problem is that the fasteners must be carefully installed to ensure that they are not over-torqued. Continued twisting of the threaded bolt or screw after the anchoring mechanism has contacted the inner surface of the wall will cause the anchoring mechanism to twist and dig into the inner surface of the wall. This digging action gouges the periphery of the wall hole, which causes the fastener to fit loosely within the wall and thereby increases the likelihood that the fastener will become dislodged from the wall.
Additionally, the supporting capacity/strength of conventional fastening structures is limited by a relatively short axis of rotation in the axial plane. As will be readily appreciated by those skilled in the art, this axis is defined by the distance between the points of support provided by the anchoring assembly and threaded member. In the case of prior art configurations such, for example, as the "moly" bolt, this distance is equivalent to the thickness of the wall or wallboard and is typically far too short to support large or heavy objects due to the high concentration of stresses over such a small area. Blind fasteners of this type will generally support a vertical weight of about 30 lbs in 1/2 inch thick drywall, at a distance of 0 to 1/2 in from the wall surface.
Another type of blind fastener, the rivet, is most often used where two or more overlapping planar elements are to be joined. For example, in the construction of modem aircraft, rivets are typically used to join the individual sheets of aluminum that collectively form a skin over the air frame. In such an environment, it is usually permissible for the adjacent rivets to be separated by the preferred spacing of one rivet diameter. Rivets have also be employed in the construction of more advanced aircraft that require the joining of complex control surfaces of graphite or other composite materials. Due to stress concentrations adjacent the holes in such materials, however, the inter-rivet spacing must be increased to four rivet diameters--thereby limiting the joining forces that may be applied. Extremely close tolerances must also be observed in order to ensure a reliable attachment.